Many modern consumer electronic devices, such as televisions, set-top boxes, digital video recorders (DVRs), digital video disk (DVD) players, etc., support High-Definition Multimedia Interface (HDMI) for connecting with other devices. HDMI is an audio/video (A/V) interface used for transmitting uncompressed digital data. Many devices have multiple HDMI ports, allowing such devices to be connected to two or more other HDMI-compatible devices.
A device that transmits data to another device is referred to as a “source” or “source device”, whereas a device which receives data from another device is referred to as a “sink” or “sink device”. A device can be both a source and a sink. Some source devices that use HDMI may encrypt the data they transmit over an HDMI interface by using High-bandwidth Digital Content Protection (HDCP). HDCP is a protocol for preventing the copying of digital A/V content as it travels across a connection, such as an HDMI link or other type of audio/video link. A connected sink device in that case must also implement HDCP and must first be authenticated by the source, to be able to decode and play the received data stream.
The use of HDCP by a sink device with multiple HDMI ports can have undesirable side effects from the perspective of a user. Consider, for example, that a user may have multiple HDMI sources concurrently connected to a given sink device, where each source is connected to a different HDMI port on the sink device. This type of configuration allows the user to switch easily from one source to another, for example, to switch back and forth between a cable box and a DVD player as the A/V source for a television (the sink). In this scenario the port that is connected to the currently selected source at any given point in time is called the “active port”.
Whenever an HDMI sink device that implements HDCP switches between HDMI ports (i.e., selects a different HDMI port as the active port), the sink and the source perform an HDCP authorization routine, which must be completed successfully before the sink can play (or otherwise decode and use) the received data. The authorization routine can take several seconds to complete. During the authorization routine the user often experiences a noticeable delay, such as a blank screen if the sink is a television. Such a delay can be annoying to the user.